Schiff bases, named after Nobel Prize winner Hugo Schiff, are compounds having the general structure R2C═NR′. A bis-Schiff base refers to a compound having at least two Schiff base components in the compound. Schiff bases are known to be useful intermediates in making catalysts, dyes, and polymers for wide variety of photo-chemical, electronic, opto-electronic, and photonic applications.
Conventional chemical processes to make bis-Schiff base compositions, such as bis-Schiff resins or its related polymer products, involve large quantities of organic solvent during synthesis and often require the use of catalysts and/or other polymerizable functional groups. Moreover, the processes often have multiple steps and laborious purification processes. Bis-Schiff bases having epoxy functionalities may require additional curing agents and mixing processes to properly cure. As such, Schiff bases are not typically economically viable as a resin product for the large-scale production of polymers or polymer composites.
Additionally, bis-Schiff bases of aliphatic aldehydes are readily polymerizable and unstable. Bis-Schiff bases of aromatic aldehydes and aromatic amines are more stable, but more difficult to process, particularly for those with polyaromatic moieties, due to their higher melting points. When bis-Schiff base compositions are used as liquid resins, for instance, in molding or coating processes, the compositions must have viscosities that are malleable enough to manipulate. Typically, the composition would be heated until the appropriate viscosity was achieved, and the resin would be applied on a mold or a substrate. However, conventional bis-Schiff bases may begin to undergo further reactions, polymerizing and/or crosslinking when in a melted state due to their high melting point. This results in rapid increases in viscosity and gelation that prevent the resin from being processed into the desirable product form and shape.